1. Field of the Invention
The present invention relates to a temperature sensor and a method of detecting temperature, and more particularly, to a temperature sensor and a related method capable of detecting a wide range of temperature.
2. Description of the Prior Art
A circuit system such as an integrated circuit (IC) is usually equipped with temperature sensor(s) to detect the temperature of the circuit system, in order to take proper measures based on the detected temperature. For example, high temperature or overheat protection is a general function of the circuit system operated based on the temperature, where several or all modules of the circuit system may be shut down when the temperature is determined to be higher than a threshold. Therefore, a temperature sensor with high temperature detection capability is necessary in the circuit system.
The operations of a display system are also determined based on the detected temperature since the characteristics of the display panel is influenced by the ambient temperature. For example, the physical characteristics of the liquid crystal may become worse under a low temperature such as below 0° C., where the drifting speed of the liquid crystal molecule becomes slower when the temperature is extremely low. Therefore, a temperature sensor with low temperature detection capability is necessary in the display system.
In general, the temperature sensor is implemented by generating a positive temperature coefficient (PTC) voltage or a negative temperature coefficient (NTC) voltage. Take the PTC voltage as an example. In order to realize the abovementioned high temperature and low temperature detection capabilities, the detectable temperature range of the temperature sensor should be quite large, such as from −30° C. to 80° C. However, the voltage range in the circuit system is limited, such that the slope of the temperature coefficient (i.e., voltage versus temperature) of the temperature sensor cannot be too oblique; that is, the voltage variation cannot be too large in response to temperature variation.
Please refer to FIG. 1A, which is a schematic diagram of the temperature sensing characteristics of a conventional temperature sensor. FIG. 1A illustrates the temperature sensing characteristics with a voltage-temperature curve (V-T curve) VPTC1. As shown in FIG. 1A, the detectable temperature range is the linear region of the V-T curve VPTC1, e.g., the temperatures T1 and T2 are detectable based on the comparison of the V-T curve VPTC1 with the ZTC voltages VZTC1 and VZTC2. The upper limit of the V-T curve VPTC1 is VDD-VOV, where VDD denotes the supply voltage of the temperature sensor and VOV denotes the overdrive voltage of the high-side transistors in the temperature sensor. When the temperature becomes higher, the V-T curve VPTC1 approaches its upper limit VDD-VOV and enters the nonlinear region where the temperature is not detectable.
In order to extend the detectable temperature range of the temperature sensor, the slope of the V-T curve may be decreased, as shown in FIG. 1B. The V-T curve VPTC2 has a smaller slope and thus has a larger detectable temperature range. In such a situation, the voltage variation becomes smaller in response to temperature variation, such that the noise immunity and offset resistance of the temperature sensor may become worse, which results in a heavy burden on circuit design. For example, if the slope of the V-T curve VPTC1 is 25 mV/5° C. and the tolerable temperature error is 1° C., the voltage error of the temperature sensor should be within 5 mV under the non-ideal factors of the circuitry. If the slope of the V-T curve VPTC2 is decreased to 5 mV/5° C. and the tolerable temperature error is still 1° C., the voltage error of the temperature sensor is requested to be within 1 mV, which significantly increases the difficulty and burden on the circuit design. Thus, there is a need for improvement over the prior art.